3 Answers
3

"En" can be either a pronoun (to replace a nominal group starting with de/du/de la/des) or a preposition (related to place/manner/matter/material).
Here I actually have trouble seeing which one it is (although I'm French :-O).

En is a complicated word. In this form, it is a pronoun with no antecedent, which is a bit of a strange concept (I think some grammars classify it as a particle, i.e. a word that doesn't fall into any neat classification). This happens in a number of idioms.

En être à means “to have reached the stage when”.

Nous n’en sommes pas encore à évoquer une quelconque date de lancement de la LTE Advanced dans l’hexagone.We have not reached the point where we might discuss a launch date for LTE Advanced in France.